DTIC ADA440259: Aquifer Susceptibility in Virginia: Data on Chemical and Isotopic Composition, Recharge Temperature, and Apparent Age of Water from Wells and Springs, 1998-2000

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U.S. Department of the Interior
U.S. Geological Survey
Aquifer Susceptibility in Virginia: Data on Chemical
and Isotopic Composition, Recharge Temperature,
and Apparent Age of Water from Wells and Springs,
1998-2000
Open-File Report 03-246
Prepared in cooperation with:
Virginia Department of Health
Office of Drinking Water
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Aquifer Susceptibility in Virginia: Data on Chemical and Isotopic
5b. GRANT NUMBER
Composition, Recharge Temperature, and Apparent Age of Water from
Wells and Springs, 1998-2000 5c. PROGRAM ELEMENT NUMBER
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Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
U.S. Department of the Interior
U.S. Geological Survey
Aquifer Susceptibility in Virginia: Data on Chemical
and Isotopic Composition, Recharge Temperature,
and Apparent Age of Water from Wells and Springs,
1998-2000
By David L. Nelms and George E. Harlow, Jr.
Open-File Report 03-246
Prepared in cooperation with:
Virginia Department of Health
Office of Drinking Water
Richmond, Virginia
2003
U.S. DEPARTMENT OF THE INTERIOR
GALE A. NORTON, Secretary
U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director
The use of trade or product names in this report is for identification purposes
only and does not constitute endorsement by the U.S. Government.
For additional information write to: Copies of this report can be purchased from:
District Chief U.S. Geological Survey
U.S. Geological Survey Branch of Information Services
1730 East Parham Road Box 25286, Federal Center
Richmond, VA 23228 Denver, CO 80225-0286
[email protected]
Information about water resources in Virginia is available on the World Wide Web at http://va.water.usgs.gov
CONTENTS
Abstract ....................................................................................................................................................................................................... 1
Introduction ................................................................................................................................................................................................ 1
Purpose and scope ........................................................................................................................................................................ 1
Definition of apparent age ............................................................................................................................................................ 3
Sampling locations ......................................................................................................................................................................... 3
Acknowledgments ......................................................................................................................................................................... 12
Sample collection, analytical methods, and quality assurance ........................................................................................................ 12
Water chemistry ............................................................................................................................................................................. 12
Major dissolved and noble gases ................................................................................................................................................ 15
Chlorofluorocarbons ...................................................................................................................................................................... 15
Sulfur hexafluoride ......................................................................................................................................................................... 15
Tritium ............................................................................................................................................................................................... 17
Tritium/helium-3 and noble gases ............................................................................................................................................... 17
Isotope ratios of carbon in water ................................................................................................................................................ 18
Stable isotope ratios of oxygen and hydrogen in water .......................................................................................................... 18
Quality assurance .......................................................................................................................................................................... 20
Analytical and quality assurance data .................................................................................................................................................. 20
Water chemistry ............................................................................................................................................................................. 20
Major dissolved and noble gases, recharge temperature, and excess air .......................................................................... 20
Chlorofluorocarbon concentrations and apparent ages ......................................................................................................... 21
Sulfur hexafluoride concentrations and apparent ages .......................................................................................................... 21
Tritium, helium, and neon data, and apparent tritium/helium-3 ages .................................................................................... 21
Carbon isotope data and adjusted radiocarbon ages .............................................................................................................. 22
Stable isotope ratios of oxygen and hydrogen in water .......................................................................................................... 23
Quality assurance .......................................................................................................................................................................... 23
References cited ....................................................................................................................................................................................... 24
Figures
1. Map showing location of wells and springs sampled in Virginia, 1998-2000 .................................................................... 2
2. Hydrogeologic section representing conceptualization of the Virginia Coastal
Plain Province as vertically layered aquifers and confining units and the regional
aquifer system classification used during the Virginia Aquifer Susceptibility .................................................................. 4
3-7. Photographs showing:
3. Connections to sample tap on discharge line (A) and at the wellhead (B)................................................................ 13
4. Flow chamber used to collect radon-222 sample .......................................................................................................... 16
5. Collection of dissolved gas samples ................................................................................................................................ 16
6. Collection of chlorofluorocarbon age-dating samples ................................................................................................. 17
7. Collection of tritium/helium-3 age-dating samples ........................................................................................................ 18
8. Graph showing sample volume requirements for carbon isotope analysis by accelerator
mass spectrometry ...................................................................................................................................................................... 9
Tables
1. Distribution of wells and springs sampled as part of the Virginia Aquifer Susceptibility study
by regional aquifer system and aquifer, 1998-2000 ................................................................................................................ 5
2. Site and well-construction information for wells and springs sampled in Virginia, 1998-2000 ...................................... 6
3. Measurement accuracy and stability criteria for water-quality field properties during purging .................................. 14
Contents III
4. Detection limits, measurement precisions, and analytical methods for water samples analyzed
for water chemistry at the USGS laboratory in Reston, Virginia ......................................................................................... 14
5. Summary of water-quality field properties and major-element chemistry in water samples ........................................ 28
6. Summary of minor-element chemistry, nitrate (NO +NO ), dissolved organic carbon, and radon-222
2 3
in water samples ......................................................................................................................................................................... 35
7. Summary of trace-element chemistry in water samples ...................................................................................................... 40
8. Summary of averaged dissolved gas compositions (nitrogen, argon, oxygen, carbon dioxide,
methane, helium, and neon), recharge temperatures, and quantities of excess air in water samples ....................... 45
9. Summary of averaged chlorofluorocarbon concentrations1 and calculated atmospheric partial
pressures in water samples ...................................................................................................................................................... 53
10. Concentrations of chlorofluorocarbons and sulfur hexafluoride in North American air, 1930-2000 ............................. 58
11. Summary of average chlorofluorocarbon-based apparent recharge dates, ages, and uncertainties
in water samples ......................................................................................................................................................................... 59
12. Summary of averaged sulfur hexafluoride data in water samples ..................................................................................... 64
13. Summary of tritium, dissolved helium, and dissolved neon data in water samples ......................................................... 72
14. Summary of apparent tritium/helium-3 ages in water samples ........................................................................................... 77
15. Summary of carbon isotopic data of dissolved inorganic carbon in water samples ....................................................... 82
16. Summary of radiocarbon ages of dissolved inorganic carbon in water samples ............................................................ 87
17. Summary of oxygen (δ18O) and hydrogen (δ2H) isotopic data in water samples ............................................................. 95
18. Summary statistics of relative percent difference between analytical data for original and
duplicate water samples ............................................................................................................................................................ 100
19. Summary statistics of analytical data for blank water quality assurance samples.......................................................... 101
IV Contents
CONVERSION FACTORS, DATUM, AND ABBREVIATED WATER-QUALITY UNITS
Multiply By To obtain
Length
inch (in.) 25.4 millimeter
inch (in.) 2.54 centimeter
foot (ft) 0.3048 meter
mile (mi) 1.609 kilometer
Area
square mile (mi2) 259.0 hectare
square mile (mi2) 2.590 square kilometer
Volume
gallon (gal) 3.785 liter
gallon (gal) 0.003785 cubic meter
Cubic inch 16.387 cubic centimeters
picocurie per liter 37.04 becquerel per liter
picocurie per liter 0.3135 tritium unit (TU)
ounce 28.35 gram
pound 0.4535 kilogram
picogram 1x10-12 gram
femtogram 1x10-15 gram
Water temperature is reported in degree Celsius (°C), which can be converted to degree Fahrenheit (°F) by the following
equation: °F = 1.8 (°C) + 32
Stable isotope ratios are reported as δ values computed from the formula
R
δ = ⎛--------x----–1⎞1,000
x ⎝R ⎠
STD
where Rx is the ratio of the isotopes measured in the sample and RSTD is the isotope ratio in the reference standard. The value of δx is in parts per thousand (per
mil).
Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29); horizontal coordinate information is referenced to the
North American Datum of 1927 (NAD27).
Abbreviated water-quality units: Chemical concentration is reported in milligrams per liter (mg/L) or micrograms per liter (µg/L). Milligrams per liter is a unit
expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water. One thousand micrograms per
liter is equivalent to one milligram per liter. For concentrations less than 7,000 mg/L, the numerical value is the same as for concentrations in parts per million.
Specific electrical conductance of water is reported in microsiemens per centimeter at 25 degrees Celsius (µS/cm).
Additional abbreviated units used in this report: L (liter), mL (milliliter), kg (kilogram), pg (picogram), fmol (femtomole), pptv (parts per trillion by volume), STP
(standard temperature and pressure, 0 degrees Celsius and 1 atmosphere), cc/L (cubic centimeters per liter).
Contents V
Aquifer Susceptibility in Virginia: Data on Chemical and
Isotopic Composition, Recharge Temperature, and Apparent
Age of Water from Wells and Springs, 1998-2000
By David L. Nelms and George E. Harlow, Jr.
ABSTRACT study between 1998 and 2000 to determine the suscep-
tibility to contamination from near-surface sources of
The determination of aquifer susceptibility the regional aquifers in Virginia that serve as public
to contamination from near-surface sources by the water supplies (Harlow and others, 1999). Water sam-
use of ground-water dating techniques is a critical ples were collected from 145 wells and 6 springs in
various hydrogeologic settings across the Common-
part of Virginia's Source Water Assessment
wealth (fig.1). Multiple environmental tracers–chlo-
Program. As part of the Virginia Aquifer
rofluorocarbons (CFCs), sulfur hexafluoride (SF ),
Susceptibility study, water samples were collected 6
tritium (3H), and tritium/helium-3 (3H/3He) and carbon
between 1998 and 2000 from 145 wells and 6
isotopes–carbon-14 (14C) and carbon-13 (δ13C) were
springs in various hydrogeologic settings across
used to estimate the age of water discharging from
the Commonwealth. Samples were analyzed to
wells and springs. Most of these wells and springs are
determine water chemistry–including nitrate
regulated as public water supplies and are classified as
(NO ), dissolved organic carbon (DOC), and
3 community, transient non-community, or non-transient
radon-222 (222Rn), major dissolved and noble
non-community systems on the basis of type of water
gases–nitrogen (N ), argon (Ar), oxygen (O ),
2 2 usage and population served.
carbon dioxide (CO2), methane (CH4), helium The Federal Safe Drinking Water Act (SDWA)
(He), and neon (Ne), environmental tracers– Amendments of 1996 require each state to develop and
chlorofluorocarbons (CFCs), sulfur hexafluoride implement a comprehensive Source Water Assessment
(SF ), tritium (3H), and tritium/helium-3 (3H/3He), Program (SWAP). The VAS study is part of the Com-
6
carbon isotopes–carbon-14 (14C) and carbon-13 monwealth of Virginia’s SWAP, which is coordinated
(δ13C), and stable isotopes of oxygen (δ18O) and by the VDH, Office of Drinking Water (Virginia
Department of Health, 1999). The premise of the VAS
hydrogen (δ2H). The chemical and isotopic
study was that ground-water age determinations can be
composition, recharge temperatures, and apparent
used as a guide for classifying regional aquifer systems
ages of these water samples are presented in this
in terms of their susceptibility to near-surface contami-
report. Data collected between 1999 and 2000
nation. The information from the VAS study will be
from 18 wells in Virginia as part of two other
used by VDH (1) to determine which water supplies are
studies by the U.S. Geological Survey also are
sensitive to contamination from near-surface sources,
presented. Most of the sites sampled serve as
and (2) to identify public ground-water supplies that
public water supplies and are included in the require detailed source water assessments.
comprehensive Source Water Assessment Program
for the Commonwealth.
Purpose and Scope
The purpose of this report is to present data col-
INTRODUCTION
lected during the VAS study from 1998 to 2000 across
the Commonwealth. Additional data that were col-
The U.S. Geological Survey (USGS), in coopera-
lected by the USGS between 1999 and 2000 to supple-
tion with the Virginia Department of Health (VDH),
ment the VAS data are presented: (1) the USGS’s
conducted the Virginia Aquifer Susceptibility (VAS)
Virginia Beach Shallow Ground-Water study, in coop-
Abstract 1
2
A
q
u
ife
r S
us 83˚ 82˚ 81˚ 80˚ 79˚ 78˚ 77˚ 76˚
c
e
p
tib
ility in 40˚ COMMONWEALTH OF VIRGINIA
V
irgin EXPLANATION
ia, 1 REGIONAL AQUIFER SYSTEM
998-200 AVaplpleayla acnhdia Rni dPglaet eCaaurbsonate and Siliciclastic VR-24 BR-1M0ARYLAND
0
PD-24
Blue Ridge
39˚ Piedmont with Mesozoic Basins (dark green) VR-17 BR-06BR-07 WASHINGTON, D.C.
VR-16 PD-23
VR-25
Coastal Plain Shallow, Middle, and Deep CP-31
A VR-09
AP-01 VIRGINIA AQUIFER SUSCEPTIBILITY STUDY WELL AND NUMBER GINI VR-10 VR-08 PD-17 Line CP-35
VIR VR-02 VR-01 PD-16
CP-50 VIRGINIA AQUIFER SUSCEPTIBILITY STUDY SPRING AND NUMBER VR-18 VVRR--0067 VR-11 PD-22 CP-03
PD-20 CP-01 CP-41
VB-01 CAINTDY ONFU VMIRBGERINIA BEACH SHALLOW GROUND-WATER STUDY WELL WEST VRV-RV2-R74-546 VR-04VVRR--0437 BR-01 PD-19 PD-13 PD-21 CCPP--3209 CP-07 CP-42 CCCPPP---111345
38˚ VTDW-01 VFRIRAGCITNUIARE PDO-LRYOTCEKC HHNYDICR IONLSOTGITYU RTEES AEANRDC SHT ASTTEU DUYN WIVEERLLSITY VVRR--3135 VR-V2R6-20 BR-03 BR-02 PD-06PD-14 CP-28 CP-23 CP-10 CP-08
AND NUMBER VR-34 VR-05 PD-07 PPDD--3105 CP-39CPC-P37-38 CP-06 CP-0C5P-49 CP-16
37˚ VR-28 APA-A0PP5--1132 AKAPEP-0N-A4T0AP7U-PC0-K61Y0AP-1AA1APPVP--00R-901-237 APV-R08-3V5R-3A1VVPRVR-V0-R-33R1-823-362VVVRRVR--R-441-24339 VVVRRR-4--B44301RV-R0-822BVVRRR---022431VRB-R1P-9B0D9R-0-025 PD-26 PPDD-0-41PP1DD--1005PD-03 PPDDP--D20-982P8D-1P2D-0Fall1 CCCCPPPP-5---03C34346PC-P4C8-C1PCC9P-PCCP3--P64P-0C4-7-4001P2CC8-P3PC2--2C2P45P-4-320CCPCCP-PP5V--2-1B22C671-P0C-71VVP1BB-0--91134 CP-VVC1BB2PV---B001V56-70B3-04
TENNESSEVER-29 VR-30 VR-14 VVVVTTTTDDDDWWWW----00001337ABA PD-25 NORTH CPADR-O27LINA PD-18 PD-0C9P-22 CP-44 CVPB--4058 VVBB--0190 VVBBVVBB--11--120012
VTDW-07B
VTDW-08
Province boundaries modified from Virginia
Division of Mineral Resources (2003).
Figure 1. Location of wells and springs sampled in Virginia, 1998-2000.
eration with the City of Virginia Beach (Johnson, 1999) example, the public water supply data base did not con-
and (2) Virginia Polytechnic Institute and State Univer- tain any springs located in the Virginia Coastal Plain
sity’s (VPI&SU) fractured-rock hydrology research for the duration of the VAS study; therefore, spring
project in Floyd County, Va. The chemical composition CP-50 was selected to assess the susceptibility to con-
of water from the wells and springs sampled is repre- tamination of springs in the Coastal Plain.
sented by data for water-quality field properties (dis- For the purpose of this study, the Commonwealth
solved oxygen, water temperature, pH, and specific was subdivided into eight regional aquifer systems on
conductance), major-, minor- (including nitrate (NO ), the basis of (1) physiographic province (Fenneman,
3
dissolved organic carbon (DOC), and radon-222 1938), (2) geologic province, and (3) hydrogeologic
(222Rn)), and trace-element chemistry, and by data for characteristics; as well as (4) major rock type (Valley
major dissolved and noble gases (nitrogen (N ), argon and Ridge province), and (5) depth of the top of the
2
(Ar), oxygen (O ), carbon dioxide (CO ), methane first screened interval (Coastal Plain province). These
2 2
regional aquifer systems are:
(CH ), helium (He), and neon (Ne)). The isotopic com-
4
1. Appalachian Plateaus,
position is represented by data for the stable isotopes of
oxygen (δ18O) and hydrogen (δ 2H). Recharge tempera- 2. Valley and Ridge Carbonate,
ture estimates from N -Ar data and quantities of excess
2
3. Valley and Ridge Siliciclastic,
air from N -Ar and Ne data are presented. Apparent
2
ages of the water samples presented in this report were
4. Blue Ridge,
estimated from multiple environmental tracers (CFCs,
SF , 3H, and 3H/3He) and 14C. 5. Piedmont (including the Mesozoic Basins),
6
6. Coastal Plain-Shallow (depths less than 200feet
below land surface),
Definition of Apparent Age
7. Coastal Plain-Middle (depths between 200 and
The term "apparent age", as defined by Plummer
400 ft below land surface), and
and Busenberg (2000), is used throughout this report
because the model age approximates the time elapsed 8. Coastal Plain-Deep. (depths greater than 400ft
since a water sample was isolated from air in the unsat- below land surface).
urated zone during recharge and is based on an inter-
The carbonate rocks in the Valley and Ridge prov-
pretation of measured concentrations of environmental
ince have different hydrogeologic characteristics (karst
tracers in ground water. Chemical (sorption and bio-
topography, solution channels, and caves) from the
degradation) and physical (mixing) processes can alter
siliciclastic rocks (sandstone, shale, and siltstone). In
the concentrations of the tracers in ground water and
the Coastal Plain province, the wedge-like geometry of
thus the model ages (Plummer and Busenberg, 2000).
the deposits results in multiple regional aquifer system
The apparent age represents estimates from the individ-
designations for a single aquifer (fig.2) based on
ual environmental tracer and does not constitute the
hydrogeologic setting (Nelms and Harlow, 2000). For
final age assigned for the water sample. The final ages
example, the Middle Potomac aquifer is initially
will be presented in the interpretive publication.
assigned to the Coastal Plain-Shallow system near the
Fall Line. As the aquifer progressively becomes deeper
Sampling Locations towards the east and less connected to hydrologic and
anthropogenic activities at the surface, the designation
Public water supplies were the primary focus of the changes; the Middle Potomac aquifer is assigned to all
VAS study. Sites were selected on the basis of (1) their three of the Coastal Plain regional aquifer systems
geographic position within the Commonwealth and (fig.2). The distribution of sites sampled during the
within the respective geologic province, (2) the avail- VAS study by regional aquifer system and aquifer is
ability of well-construction information, and (3) their summarized in table1.
accessibility (fig.1). Additional sites (19 wells and 1 Site and construction information for wells and
spring) that are not classified as public water supplies springs sampled between 1998 and 2000 are summa-
also were selected based on unique characteristics. For rized in table2. Latitudes and longitudes were deter-
Introduction 3